Add method to check whether Deferred Stats are present. (envoyproxy#3…

…3877)

Commit Message: Add method to check whether Deferred Stats are present.
Risk Level: low
Testing: unit
Docs Changes: none
Release Notes: none

Signed-off-by: Paul Ogilby <[email protected]>

envoy/stats/stats.h

@@ -231,9 +231,20 @@ Envoy
  */
 template <typename StatsStructType> class DeferredCreationCompatibleInterface {
 public:
-  // Helper function to get-or-create and return the StatsStructType object.
+  /**
+   * Returns an already existing StatsStructType, or creates a new one and returns it.
+   *
+   * @return The new or already existing StatsStructType.
+   */
   virtual StatsStructType& getOrCreate() PURE;
 
+  /**
+   * Returns whether or not the underlying stats have been initialized yet.
+   *
+   * @return If the underlying stats have been initialized.
+   */
+  virtual bool isPresent() const PURE;
+
   virtual ~DeferredCreationCompatibleInterface() = default;
 };
 
@@ -250,6 +261,13 @@ template <typename StatsStructType> class DeferredCreationCompatibleStats {
   inline StatsStructType* operator->() { return &data_->getOrCreate(); };
   inline StatsStructType& operator*() { return data_->getOrCreate(); };
 
+  /**
+   * Returns whether or not the underlying data_ has been initialized yet.
+   *
+   * @return If the underlying data_ has been initialized.
+   */
+  bool isPresent() const { return data_->isPresent(); }
+
 private:
   std::unique_ptr<DeferredCreationCompatibleInterface<StatsStructType>> data_;
 };

source/common/common/thread.h

@@ -139,6 +139,14 @@ class AtomicPtrArray : NonCopyable {
     return atomic_ref.load();
   }
 
+  /**
+   * Returns whether the underlying pointer at the index is null.
+   *
+   * @param index the Index to look up.
+   * @return true if the underlying pointer at the index is null.
+   */
+  bool isNull(uint32_t index) const { return data_[index].load() == nullptr; }
+
 private:
   std::atomic<T*> data_[size];
   absl::Mutex mutex_;
@@ -166,6 +174,11 @@ class AtomicPtr : private AtomicPtrArray<T, 1, alloc_mode> {
    * @return The new or already-existing T*, possibly nullptr if make_object returns nullptr.
    */
   T* get(const MakeObject& make_object) { return BaseClass::get(0, make_object); }
+
+  /**
+   * @return true if the underlying pointer is null.
+   */
+  bool isNull() const { return BaseClass::isNull(0); }
 };
 
 // We use platform-specific functions to determine whether the current thread is

source/common/stats/deferred_creation.h

@@ -55,6 +55,7 @@ class DeferredStats : public DeferredCreationCompatibleInterface<StatsStructType
     }
   }
   inline StatsStructType& getOrCreate() override { return getOrCreateHelper(); }
+  bool isPresent() const override { return !internal_stats_.isNull(); }
 
 private:
   // We can't call getOrCreate directly from constructor, otherwise the compiler complains about
@@ -92,6 +93,7 @@ class DirectStats : public DeferredCreationCompatibleInterface<StatsStructType>
   DirectStats(const typename StatsStructType::StatNameType& stat_names, Stats::Scope& scope)
       : stats_(stat_names, scope) {}
   inline StatsStructType& getOrCreate() override { return stats_; }
+  bool isPresent() const override { return true; }
 
 private:
   StatsStructType stats_;

test/common/stats/deferred_creation_stats_test.cc

@@ -54,11 +54,15 @@ TEST_F(DeferredCreationStatsTest, StatsGoneWithScope) {
     MyStats x = createDeferredCompatibleStats<AwesomeStats>(scope, stats_names_, true);
     MyStats y = createDeferredCompatibleStats<AwesomeStats>(scope, stats_names_, true);
     EXPECT_EQ(TestUtility::findGauge(store_, "bluh.AwesomeStats.initialized")->value(), 0);
+    EXPECT_FALSE(x.isPresent());
     x->foo_.inc();
     EXPECT_EQ(TestUtility::findGauge(store_, "bluh.AwesomeStats.initialized")->value(), 1);
+    EXPECT_TRUE(x.isPresent());
+    EXPECT_FALSE(y.isPresent());
     EXPECT_EQ(x->foo_.value(), 1);
     EXPECT_EQ(y->foo_.value(), 1);
     EXPECT_EQ(TestUtility::findGauge(store_, "bluh.AwesomeStats.initialized")->value(), 2);
+    EXPECT_TRUE(y.isPresent());
   }
   // Deleted as scope deleted.
   EXPECT_EQ(TestUtility::findCounter(store_, "bluh.foo"), nullptr);
@@ -68,11 +72,13 @@ TEST_F(DeferredCreationStatsTest, StatsGoneWithScope) {
     ScopeSharedPtr scope = store_.createScope("bluh");
     EXPECT_EQ(TestUtility::findGauge(store_, "bluh.AwesomeStats.initialized"), nullptr);
     MyStats x = createDeferredCompatibleStats<AwesomeStats>(scope, stats_names_, true);
+    EXPECT_FALSE(x.isPresent());
     EXPECT_EQ(TestUtility::findGauge(store_, "bluh.AwesomeStats.initialized")->value(), 0);
     // Previous data is gone, as scope_v2 and scope_1's lifecycle do not overlap.
     EXPECT_EQ(x->foo_.value(), 0);
     // Initialized now.
     EXPECT_EQ(TestUtility::findGauge(store_, "bluh.AwesomeStats.initialized")->value(), 1);
+    EXPECT_TRUE(x.isPresent());
   }
 }